1. Field of the Invention
The present invention relates to a drive apparatus in which an electronic switch is connected to excite an electromagnetic solenoid.
A term "ELECTROMAGNETIC ACTUATOR" used in the title is significant of an electromagnetic solenoid, electric motor, electromagnetic relay and other actuators using an electromagnetic force.
2. Description of Related Art
A conventional apparatus for driving an actuator is shown in, for example, FIGS. 5 to 7.
As shown in FIG. 5, when a pulse signal having such a narrow width that a solenoid MV is not actuated is applied to an electronic switch Q in a drive unit via a control input terminal IN of the apparatus, the electronic switch Q is turned on or off and the voltage Vz across the surge absorber Z has a wave-form which is in phase with that of the pulse signal Vi. The actuator drive apparatus is arranged in such a manner that the voltage Vz is divided by a voltage dividing circuit including resistor elements Rs and R so that a voltage VR having an appropriate level is inputted to an inverting amplifier A to output an output signal Vo.
The solenoid MV is represented by an equivalent circuit including a resistor and an inductor. If the solenoid of the apparatus is completely broken (failure mode B), no current flows through the solenoid of the apparatus. Accordingly, since the waveform of the output signal Vo is at a continuous high level as shown in FIG. 7, a defect of the solenoid MV is detected.
If the solenoid of the apparatus is partly-broken or burnt (failure mode A), the solenoid of the apparatus is conductive, although the solenoid exhibits no electromagnetic characteristics. Accordingly, the prior art actuator drive apparatus can not determine whether or not the solenoid MV is defective because the output signal Vo has a wave-form which is substantially the same as the normal wave-form as shown in FIG. 6.